Frank plays upright bass for the Country Trio, a Muppet band that performed in variety show appearances in the mid 70s, and occasionally on The Muppet Show. Frank, and his fellow Trio members Jim and Jerry, are based on their respective performers. Bonnie Erickson, who designed and built Jim and Frank, said that "[the puppets] are dressed that way, because that's how [Jim, Frank and Jerry] dressed then."
They were created for an appearance on The Perry Como Winter Show in 1972, where they sang "You Don't Mess Around with Jim." They re-appeared on The Dick Cavett Show in 1973, singing "Momma Don't Allow." During the later appearance, the members of the Trio addressed each other as "Jim", "Frank" and "Jerry".
Frank Oz used a low, guttural voice for Frank. For his appearance on The Dick Cavett Show, when the puppeteers were interviewed with their characters, Oz spoke in a Miss Piggy-esque voice as if it were his natural voice.
On The Muppet Show, the Trio has performed "To Morrow", "In the Summertime", and "A Four-Legged Friend". Jim also sat in with the Electric Mayhem during the closing credits of The Muppet Show: Sex and Violence. Frank also made appearances in episodes 308 and 317.